Any steps taken during the manufacturing and packaging of integrated circuits (ICs) which improve wafer yield or reduce the time and resources for determining functioning dies or die characteristics is important. ICs are tested and characterized at different points during the process by which they are fabricated and packaged. The test and characterization data can be used to grade the performance of the dies which are packaged to form the ICs, and to eliminate dies that fail to meet performance (e.g., speed) standards set by a manufacturer. ICs are also referred to herein as, e.g., packaged dies or chips.
During a testing phase referred to as “wafer sort”, functional tests are typically performed on dies. At this point, the dies are fully formed, but have not yet been “diced” (separated into individual chips) or packaged. Dies are typically produced on silicon wafers, each wafer having many dies. The functional test results are analyzed, and the dies that fail to pass functional tests are discarded. After the dies are cut from the wafer and separated from each other, and after the dies that failed the wafer sort test have been eliminated, the remaining dies are assembled into their packages. The dies may be offered in many different packages. The packaging process can involve attaching bond wires or solder bumps to the I/O bonding pads of the die, connecting the die to a substrate, and enclosing the die in a protective package. Once packaging is complete, another set of tests during a “final test” phase, is performed. During the final test phase, automated test equipment (ATE) tests the performance of the fully packaged dies, and, as with the wafer sort test, dies that fail to meet the performance standards set by a manufacturer are discarded.
During the final test phase, various measurements allow the better dies to be separated from the normal or below normal performing dies. An accurate and repeatable test system can sort the individual die into speed categories in a process generally referred to as speed binning. That is, a die is assigned a bin number based upon the results of a series of tests, where the bin number provides an indication of the speed of the die. For example, a die that passes all high-speed tests would be placed in a different bin indicative of faster operating characteristics, such as operating frequency. Speed binning is typically used to identify packaged dies that can operate at frequencies in excess of a baseline frequency for sale at a premium price.
Manufacturers packaging and selling high performance dies may, after speed binning, be left with many low performance dies which cannot be sold to the customer requesting high performance dies and thus will be kept in inventory until another customer requests dies with lower performance requirements and the same packaging. Because speed binning is done on packaged dies, those lower performing dies have a high inventory cost because packaged dies typically depreciate about 30% per year. Because of the high inventory costs of packaged dies, a manufacturer will be more profitable if it keeps its unsold inventory of packaged dies to a minimum.
Therefore, it is desirable to minimize the number of lower performing dies that are packaged when manufacturing and fulfilling orders for high performance dies.